PAG for organic chemistry

Question 1

distillation

Answer 1

• used to separate an organic reaction mixture
• bottom of condenser is connected to the cold water supply and the top of the connector is connected to a hose that drains water into the sink,
• antibumping granules are added to ensure smooth boiling
• mixture is heated, and as the product is collected the temperature on the thermometer can be used to identify the chemical

Question 2

heating under reflus

Answer 2

• pear shaped flask
• heating mantle
• condesner - cold water enters bottom and cold water leaves through the top -
• ensures volatile compounds are not lost from the reaction mixture
• volatile reagents are returned to the reaction mixture rather than escaping before they can react

Question 3

filtration under reduced pressure

Answer 3

• connect thick walled rubber tubing to the vacuum pump and check there is suction
• put a buchner funnel into the top of the filter flask, for small quantites a hirsch funnel can be used
• connect tubing from the vacuum pump to the side arm of the clamped filter flash and start the suction
• place a piece of filter paper on top of the funnel
• use distilled water to dampen the filter paper so it sticks over the holes of the funnel
• pour reaction mixture into the centre of the funnel
• wash out the reaction vessel and the funnel with the solvent and add this to the funnel
• rinse the collected solid with more solvent and maintain suction for a minute after all the washings have been added
• turn of suction, remove tube from side arm
• invert the funnel onto a watch glass and collect the organic solid

Question 4

recrystallisation

Answer 4

• crude product is dissolved into the minimum volume of hot solvent, hot solvent is used as the solubility of solids is higher, if the product is coloured activated charcoal can be heated with the mixture to remove the coloured impurities
• hot solution should then undergo gravity filtration using fluted filter paper,
• hot filtrate should be allowed to cool this reduces the solubility and crystals of the product will form, if no crystals appear to be forming scratch the sides of the conical flask with a clean glass rod can form nucleation sites and help crystalisation
• or cool in ice bath to speed up
• any solbule impurities remain dissolved
• purified organic product can be collected by vacuum filtration, crystals should be washed with a samm amount of cold solvent to remove any of the filtrate which contains dissolved impurities

Question 5

measuring melting points

Answer 5

melting point apparatus

• in sealed capillary tube put a few grains of the organic solid, insert the tube into a melting point machine and add accurate thermometer with a suitable range
• swiitch on the machine and turn the heating dial to 4, for lower melting point compounds do not be tempted to use a higher setting or boost the function as you will miss the melting point
• look through the lens and watch the crystals, when they start to fall away from the sides of the capillary tube melting has begun, record this temperature and watch until sample has liquefied then note the new temperature this is the melting point range

thiele tube

• in a sealed capillary tube put a few grains of organic solid, use a small rubber band and attach the tube to a thermometer, submerge the thermometer into the oil of the thiele tube ensuring that the rubber band is above the oil line
• heat side arm of the thiele tube

Question 6

using a separation funnel

Answer 6

• mount an iron ring on a clamp stand and put the separating funnel in it
• remove the stopper and make sure that the tap at the bottom is closed
• pour the mixture into the funnel so that the funnel is no more than half full, wash out the reaction vessel with water and add this to the mixture in the funnel, there should still be some air in the funnel, put the stopper back
• take the funnel out of the ring and invert it, open teh tap to equalise pressure, turn the tap back to closed and shake the mixture in the funnel and equalise the pressure as required, repeat until you no longer hear a whistle
• replace teh funnel in the iron ring and give the mixture time to separate into layers
• remove the stopper, put a beaker under the spout and open the tap, collected the lower water layer in a beaker, turn the tapp off and as the organic product is in the upper layer this aqeous layer can be discareded
• using a dry beaker open teh tap and collec desired product
• shake liquid with a small amount of drying agent and pour the final dry product into a clean dry cotnainer

Question 7

using drying agents

Answer 7

• used to dry
• add a few spatuals
• drying agent clumps together then add more
• when drying agent remains free the organic product is dry
• use gravity filtration and collect the filtrate which is the dry organic product

Question 8

redistillation

Answer 8

• performing mutiple distilattions